NONLINEAR RESPONSE OF BRIDGES UNDER MULTISUPPORT EXCITATION

This work presents the results of an extensive numerical study on the nonlinear response of bridges subjected to multisupport seismic excita tion. Bridges of varying stiffness and ductility have been designed bo th for nonsynchronous motion and, as in current engineering practice, for synchronous motion, and have been subsequently analyzed in the non linear range under nonsynchronous input motion. The purpose of the stu dy has been to assess the effects on the peak inelastic response of br idge structures and the extent of validity of the force reduction fact or (q-factor) approach for the design. The results show that displacem ent ductility demands in bridges designed by the q-factor method for a multisupport excitation are in good accordance with the selected valu e of q. The bridges designed for synchronous input and then checked fo r nonsynchronous motion exhibit an excess of strength in the central p iers, whereas the opposite occurs for those close to the abutments, wh ich may have displacement ductility demands larger than those requeste d under synchronous motion.